I've been kind of disappointed in the mileage of my beater. It's a '96 Grand Am GT with a 3.1. I bought it because #1 it was cheap for the condition and miles and #2 I have never had a 3.1 that got less than 27 and that was in slightly heavier cars. This one has never done better than 25 even though I took great pains to conserve gas which hasn't been easy for me because I don't like to "waste time" getting from A to B. Usually it was around 23-24. I finally said screw it and started driving it like normal for me, not crazy but I do make it work and wind it out fairly often and when I pass on the 2 lanes I try to spend as little time in the other lane as possible. Now I'm getting 27+........ WTH?!!!!!!!! I'm not complaining, just confused.

Fuel economy is affected by so many variables that variation of 10% isn't really saying much I think...

You didn't mention much about timeframe, but your increase in MPG might be seasonal. I've noticed I get better gasoline mileage with the summer gasoline blend than the winter gasoline blend. Might you be seeing something similar?

I'm with slipangle, I really see a difference in my daily beater from summer to winter. I'm not sure if its the blend or the fact that the car spends more time running rich and I'm working the blower in the winter more, but the difference is certainly more than 10% in my case. Maybe 15 or 20.

if they check out good then replace the 02 sensor only and try that out
over time the sensor gets clogged up and burnt out and cant sense any more and thinks the mixture is too lean so it over compensates by adding more fuel

i doubled the highway fuel mileage in my 4.3L by swapping the original and long dead 02 sensor out at 198k miles, and that was just with another non heated single wire one.

before i swapped it the exhaust would burn your eyes and the muffler tips(custom duals and no cat converter) were very black dry sooty.

Ahhh, and there lies one of the misconseptions of fuel savings, that it takes you longer to get somewhere. This may be true running down the innerstate at 85 as opposed to 55 but around towns where you are hitting stop lights and such, "hypermiling" for fuel economy actually gets you there faster! One of the biggest things you do in hypermiling is to time stop lights so you don't stop at them.

One of the things that could have made a difference is if you were starting off from every stop with a "glacier" start....barely....pushing....on...the....gas...a. ...little...more....and.....more until you are up to speed is you are spending more time in lower gears. If you get up to speed a little faster so your tranny has shifted up into higher gears you are going to save more fuel.

You want to play a little, check out this site. http://ecomodder.com/forum/ Some of the guys there are getting CRAZY milage from their cars.

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